1. Field of the Invention
The present invention relates to a communication apparatus configured to perform a communication via a public line network and a withstand voltage test method performed for the communication apparatus.
2. Description of the Related Art
Communication apparatuses of various types such as a telephone apparatus, a facsimile apparatus, and a set top box for CATV are each configured to be connected to a corresponding one of external public line networks to perform a communication via the public line network. In such a communication apparatus, a surge protection element such as a gas arrestor is normally connected to between a transmission line to be connected to the public line network and a frame (may be hereinafter referred to as a “frame ground”) of the communication apparatus in order to protect the inside of the communication apparatus from an excessive electric energy (i.e., a surge) flowing into the communication apparatus by a lightning strike, for example. In addition to the surge protection element, (a) a condenser for preventing a radiation noise and a static electricity, etc., and (b) various elements and circuits, etc., insulated from the public line network are generally connected to between the frame ground and the transmission line, for example.
It is noted that, as a construction in which the above-described various elements and circuits are connected to the frame ground, there is known a construction in which a terminal to be connected to the frame ground is provided on a print circuit board on which the various elements and circuits including the transmission line are mounted, and the terminal to be connected to the frame ground is brought into contact (conduction) with the frame ground by fixing the print circuit board to the frame.
The surge protection element preferably has a low discharge starting voltage in order to protect the inside of the apparatus from the surge caused by the lightning strike, for example. The use of the surge protection element having the low discharge starting voltage allows the surge protection element to react or to cause an electrical discharge in an early stage (i.e., before the voltage rises to a high level), thereby protecting the inside of the apparatus from the surge.
Meanwhile, a withstand voltage test is performed for such a communication apparatus before the communication apparatus is shipped to a market as a finished product, in order to ensure that the communication apparatus has a constant dielectric strength. Specifically, a specific test voltage (1.5 kV, for example) is applied to between the transmission line and the frame ground for a specific length of time (1 minute, for example), and an electric property therebetween such as a leakage current is measured and evaluated.
As described above, the surge protection element having the low discharge starting voltage is preferably used in order for an increase in a protection performance from the surge. However, if the surge protection element having the low discharge starting voltage (1 kV, for example) is used in the communication apparatus in order for increasing in the protection performance from the surge, the surge protection element discharges electricity in the withstand voltage test, so that the dielectric strength of the communication apparatus cannot be evaluated. That is, an improvement of the surge protection performance and a proper withstand voltage test are traded off.
In order to avoid this problem, the following test method is a possible approach, for example. That is, the withstand voltage test is performed after the surge protection element mounted on the print circuit board by soldering is temporarily removed, and then the surge protection element is mounted again on the print circuit board by soldering after the test is finished. However, such a test method leads to increases in a length of time required for the test and cost and results in an adverse effect on a quality of the product.
In order to solve this problem, there is known a technique that a connector is provided in a path extending from an AC input to a frame ground via a surge protection element in order to easily or simply perform a withstand voltage test, the connector being a connector which is easily inserted and removed and which is for conducting and interrupting the path, for example. In this technique, the withstand voltage test is performed with the connector removed and the path interrupted, and after the test is finished, the path is conducted by the reinsertion of the connector, thereby reducing the length of time required for the withstand voltage test.